Date: Sun, 17 Oct 1999 10:11:40 EDT
Reply-To: kenneth d lewis <kdlewis@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: kenneth d lewis <kdlewis@JUNO.COM>
Subject: Re: 1.9 heads on a 2.1 engine? Part II
I wrote:
> FWIW let's calculate stroke assuming the heads are the same.
>Bentley only mentions one piston for both engines; 9.4 cm in diameter.
>I come up with a stroke of 7.565cm for the 2.1L and 6.8475cm for the
>1.9L.
In actuality, calculating stroke is independent of head volume.
As a matter of fact; if pistons, cylinder length and head seal thickness
are the same in both engines the head volume MUST be different. This is
assuming a 9:1 CR in both engines. Since each piston displaces 50cc more
in the 2.1L engine, then that volume must go somewhere for the CR to
remain the same.
Is volume of each head combustion chamber 50cc bigger? I do not
know, I am only theorizing. Lets assume this theory is correct and we
proceed with calculating the CR of a 2.1L engine with 1.9L heads. If the
squish volume is reduced by 50cc we have:
CR= (525+15.625)/15.625
CR=34.6:1!!!!!!!!!!!!!
This clearly is impossible so some or all of that extra 50cc must
go somewhere. A clue is given on pages 13.44 and 13.45 of the Bentley. It
shows the dish dimensions are different between the two pistons!
Unfortunately they only gives depth measurements and not volume. So our
CR calculations are at a stand still until we have some more data. Anyone
out there have some pistons laying around they can CC?
Drive Safely & Good Luck
Ken Lewis<Kernersville,NC>86 VW crewcab;60 T-5 Coupe
On Sat, 16 Oct 1999 00:29:13 EDT kenneth d lewis <kdlewis@JUNO.COM>
writes:
>Roger;
> This is news to me. I thought both heads were the same. The
>Bentley refers to ONE head for both engines. Anyway, here are some
>formulas so you can decide for yourself. First some definitions:
>
>Squish volume= The volume in the cylinder when the piston is at top
>dead center.
>
>Cylinder volume= the volume swept by the cylinder i.e. 2.1L=525cc;
>1.9L=475cc
>
>If memory serves me compression ratio is given by the following
>formula:
>
>C.R.= (Cylinder volume+Squish volume) / Squish volume
>
>Solving for Squish volume I come up with:
>
>Squish volume= cylinder volume/ (C.R.-1)
>
>Assuming a compression ratio of 9:1 in both engine;
>
>Squish volume for the 2.1L= 65.625cc
>Squish volume for the 1.9L= 59.375cc
>
>This supports your claim of approximately 5cc difference between
>heads. Now lets recalculate using 2.1L volume and 1.9L squish volume:
>
>C.R.=(525+59.375)/59.375
>
>C.R.=9.84:1
>
>There is one important piece of data we may or may not need to take
>into account; the 2.1L has a longer stoke. So how much of that change
>in squish volume is due to different heads and how much is due to
>different stroke? I will leave that question open for debate.
>
> FWIW let's calculate stroke assuming the heads are the same.
>Bentley only mentions one piston for both engines; 9.4 cm in diameter.
>I come up with a stroke of 7.565cm for the 2.1L and 6.8475cm for the
>1.9L.
>
> That's enough math for tonite, I still have to go out and
>finish installing the relays to boost the voltage to the headlights on
>my transporter. I will mull these figures over and get back with you.
>
>
>Drive Safely & Good Luck
>Ken Lewis<Kernersville,NC>86 VW crewcab;60 T-5 Coupe
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